1. Field of the Invention
The present invention relates to a distance detector used for automatic focusing in silver halide film cameras, video cameras and still video cameras (SVC).
2. Description of the Prior Art
Conventional examples of such a distance detector include one that performs distance measurement in one line of distance measurement area 61 horizontal to a taking image plane 60 of a camera as shown in FIG. 1. The distance measurement sensor provided in the conventional distance detector is configured, for example, as shown in FIG. 2. A pair of line sensors 75 and 76 are disposed on the left and the right with a control circuit 10 in between. The line sensors 75 and 76 are situated substantially on the imaging planes of a pair of lenses disposed with a predetermined distance between the optical axes thereof. The line sensors 75 and 76 sense subject image light by means of light sensing arrays 12 comprising a plurality of light sensing elements.
Photocharges generated in the light sensing arrays 12 are successively transferred and output for each pixel by processors 11 in response to a clock supplied from the control circuit 10. Based on the output from the distance measurement sensor, a microcomputer calculates the distance to the subject.
In a distance measurement sensor shown in FIG. 3, a pair of line sensors 77 and 78 are disposed on the left and the right so as to have the same function as that of the above-described distance measurement sensor (FIG. 2). Processors 31 are disposed for each pixel on both sides with the light sensing arrays 12 in between.
However, in the above-described conventional distance detectors, since the distance measurement area 61 merely crosses the central portion of the taking image plane 60 as shown in FIG. 1, distance measurement cannot be performed when the subject 62 is situated in the lower part or in the upper part of the image plane 60.
In order to ensure the measurement of the distance to the subject 62, a configuration as shown in FIG. 4 is considered in which a plurality of lines of distance measurement areas 63 to 65 are provided so that distance measurement can be performed in a wider range. In this configuration, the shorter the distance D1 between the distance measurement areas 63 to 65 which the line sensors face is, the more distance measurement areas can be provided in the taking image plane 60 and the more the detection of the subject 62 is ensured. Since the subject 62 can be detected by use of a multiplicity of line sensors, the distance detection accuracy can be improved.
Distance detectors having such a plurality of lines of distance measurement areas include one having a distance measurement sensor configured as shown in FIG. 5. The distance measurement sensor shown in FIG. 5 has two pairs of lines sensors 81 to 84 and performs distance measurement along two lines.
The distance measurement sensor has the control circuit 10 at a position with respect to which the sensor is symmetrical. The two pairs of line sensors 81 to 84 are arranged so that the light sensing arrays 12 and the processors 11 accompanying them are oriented in the same direction. In the line sensors 81 to 84, reduction in the distance d7 between the light sensing arrays 12 of the line sensors is physically limited because of the existence of the processors 11.
When the focal length of the taking system is long in order to obtain a large subject image, as schematically shown in FIGS. 6A and 6B, the angle of view G of the taking optical system is generally narrow. In this case, when the distance d8 between lines sensors 91 to 93 is sufficiently short as shown in FIG. 6A, distance measurement can be performed with a distance measurement distance D2 on the taking image plane. However, when the distance d9 between line sensors 94 to 96 is long as shown in FIG. 6B, the distance measurement line density decreases because distance measurement with the distance measurement distance D2 is impossible, so that the distance measurement areas are outside the taking image plane in some cases. As a result, the reliability and the accuracy of the distance to the subject 62 deteriorate.